Default Misc Charges on a Purchase Order

We have a possible requirement to default a misc charge for all purchase orders to a specific supplier.

It looks like it can be done by item or category, and possibly by contract- although it appears in the voucher section which makes me wonder if it's not for recurring voucher contracts- but I didn't see an option on the supplier record to default a misc charge.

Do others have this requirement? If so, how do you accomplish it without touching all PO's to that supplier?

Thanks,

Wendy